CN1068130A - Monocarboxylic Acid Powder Coating Curing System - Google Patents

Abstract

A kind of powdered thermosetting compositions for coatings, it has improved apparent character and weatherproof character, as selection, elephant skin and image-testing character but (DOI), kept other physical properties simultaneously, as flexible, weather resistance, anti-solvent and resistance to abrasion, it comprises a kind of carboxylic acid group's of containing polyester, a kind of beta-hydroxy alkylamide solidifying agent that contains monocarboxylic acid based material.

Description

This invention relates to thermosetting powder coating compositions, and more particularly, to compositions having improved optical properties such as improved gloss, reduced wrinkle, and improved DOI. The powder coatings of the present invention are suitable for use as general industrial coatings, machinery and equipment coatings, especially metal coatings such as coatings for cans, utensils, automotive parts, and the like. In addition, the powder coating composition can be used for films, fibers, paints, lacquers, varnishes, seamless floors, putties and impregnations.

Powder coating compositions are known in the art to be useful in the coating of metal substrates. Such coating compositions are highly desirable because their application greatly reduces and potentially eliminates organic solvents in liquid coatings. When powder coating compositions are cured by heating, few, if any, volatile species are released into the environment, compared to liquid coatings which use organic solvents which evaporate into the atmosphere when the coating is heat cured. Coatings are very beneficial.

For exterior durability, prior art powder coating compositions are composed of a polyester or acrylic polymer containing carboxylic acid groups, a material containing dicarboxylic acid groups and a beta-hydroxyalkylamide curing agent. As formulated, these powder coating compositions and cure systems are said to be stable and have good physical properties. It is also known in the art that the powder coating curing mechanism is an important aspect of powder coating compositions. The curing system of the present invention provides improved optical properties relative to the prior art while maintaining other desirable physical properties.

The curing mechanism of the system of the present invention is derived from an acid group-containing polyester polymer, a β-hydroxyalkylamide curing agent, and a monocarboxylic acid group-containing material, which improves optical properties but has no effect on other physical properties such as flexibility. Performance, durability, solvent and corrosion resistance are not adversely affected.

According to the present invention, there is provided a thermosetting powder coating composition comprising a carboxylic acid group-containing polyester having a Tg of about 30-85°C and an acid value of about 20-80, a β- Hydroxyalkylamide curing agent and a monocarboxylic acid to improve appearance and weatherability.

The composition may also contain an epoxy functional curing agent such as triglycidyl isocyanurate (TGIC) or a mixture of TGIC and a hydroxyalkylamide curing agent. The cured powder coating composition of the present invention has improved optical properties such as gloss, wrinkle, and DOI while retaining other physical properties such as storage stability (i.e., no caking when exposed to heat), flexibility, hardness, resistance Solvent and corrosion resistance, plus other good physical properties such as hardness, impact and chemical resistance, and recoatability.

The composition may also include an acid-functional acrylic polymer, an epoxy-functional or hydroxyalkylamide curing agent, and a monofunctional carboxylic acid to improve surface properties.

The powder coating composition of the present invention comprises an intimate mixture of several materials, but three are essential components, namely, a polyester containing carboxylic acid groups, a polyester selected from aliphatic or aromatic monocarboxylic acid groups And includes the second carboxyl group of its mixture and a β-hydroxyalkylamide curing agent. The addition of monocarboxylic acid groups significantly improved optical properties such as gloss, wrinkle and DOI.

Among the polyesters containing carboxylic acid groups that may be selected are those derived from the condensation reaction of aliphatic polyols, including cycloaliphatic polyols, with aliphatic and/or aromatic polycarboxylic acids and anhydrides. Examples of suitable aliphatic polyols include 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, tris Methanol propane, etc. Suitable polycarboxylic acids and anhydrides include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 1,2 , 4-trimesic acid, and anhydrides of these acids.

The polyol and acid or anhydride are reacted together in excess of acid relative to alcohol to form a polyester with free carboxyl groups. It is preferred that the polyesters containing carboxylic acid groups have an acid value of about 20-80, more preferably about 20-45, and are solid at room temperature. The polyesters are further characterized by a Tg of about 30-85°C, preferably about 40-75°C.

The Tg of a polymer is a measure of its hardness and flowability. The higher the Tg, the less fluid and harder the coating. Tg is described in "Principles of Polymer Chemisrry (1953), Cornell Uminersity Press. Tg can be actually measured or calculated by Fox in Bull.Amer.Plysics Soc., 1,3, 123 pages (1956). Here The Tg used is the actual measured value. To measure the Tg of a polymer, differential scanning calorimetry (DSC) can be used (heating rate of 10°C per minute, taking the first pour point as Tg).

If the Tg of the polyester is below 30°C, the polymer and the powder coating composition comprising the polymer become viscous and difficult to handle. If the Tg is higher than 85°C, the melt flow of the polyester is low, and the appearance of the coating is poor.

The other essential ingredient of the powder coating composition of the invention is the beta-hydroxyalkylamide which is a curing agent for the acid-functional polyester. The β-hydroxyalkylamides can help to obtain a cross-linked polymer network that is hard, durable, corrosion-resistant and solvent-resistant. It is believed that the beta-hydroxyalkylamide cures the coating by esterification with the carboxyl-containing polyester to form multiple ester linkages. The average value of the hydroxyl functionality of the β-hydroxyalkylamides should be at least 2, preferably greater than 2, more preferably greater than 2 up to 4, for optimum curing.

In the preparation of acid group-containing acrylic polymers, the various monomers are mixed together and reacted by the usual free radical initiated polymerization method. Available free radical initiators include benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, azobis(2-methylpropionitrile) and the like. Chain transfer agents such as mercaptopropionic acid may also be used. The polymerization reaction is preferably carried out in solution, using a solvent such as toluene or xylene in which the monomer is soluble. Upon completion of the polymerization, the reaction mixture is evaporated to free volatile components by, for example, placing under vacuum to remove the organic solvent and recover the solid polymer. In addition, polymers can be precipitated and subsequently dried. Typically, the devolatilized polymer will contain less than 1% by weight of species that volatilize at the curing temperature of the coating.

The acid group-containing polymer can also be a kind of propionic acid polymer prepared by emulsion polymerization, suspension polymerization, bulk polymerization or their suitable combination, these methods are as described in U.S. Patent 4,727,111, and stated and into the present invention. These techniques are well known in the art.

The structure of β-hydroxyalkylamide can be represented by the following formula:

Wherein, R ₁ is H or C _1-5 alkyl; R ₂ is H, C _1-5 alkyl or

，其中X为2-12、最好4-10的一个数。Wherein, R ₁ is the same as above; A is a bond, monovalent or multivalent organic group, which is derived from saturated, unsaturated or aromatic hydrocarbons, including substituted hydrocarbon groups containing 2-20 carbon atoms, m is 1 to A number of 12, n is 0 or 2, m+n is at least 2, preferably greater than 2, usually between 2 and equal to 4. Preferably A is an alkylene group - (CH ₂ )

, wherein X is a number of 2-12, preferably 4-10.

The β-hydroxyalkylamides are prepared by reacting a lower alkyl ester or ester mixture of a carboxylic acid with a β-hydroxyalkylamide at a temperature between ambient temperature and about 200°C, depending on the choice of reactants and the presence or absence of a catalyst. Based on the weight of the alkyl ester, the appropriate amount of the catalyst is about 0.1-1 wt%, and the catalyst includes base catalysts such as sodium methoxide, potassium methoxide, sodium butoxide, potassium butoxide, sodium hydroxide, potassium hydroxide and the like.

For the most efficient curing of the powder coating composition, the equivalent ratio of β-hydroxyalkylamide (hydroxyl equivalent) to carboxyl-containing polyester (carboxylic acid equivalent) is preferably from about 0.6:1 to 6:1, more preferably 0.8 :1-3:1. Ratios outside 0.6:1-6:1 are undesirable because of their poor cure.

The powder coating composition may also include a material containing a monocarboxylic acid group selected from aliphatic acids including stearic acid, myristic acid, palmitic acid, phenoxyacetic acid, phenoxypropionic acid, crotonic acid, benzoic acid and mandelic acid; aromatic acids include benzoic, toluic (ortho, meta, and para), acetylsalicylic, salicylic, methoxybenzoic (anisic), cumenic, and cinnamic; cyclic Fatty acids include cyclohexane carboxylic acid, cyclopentane carboxylic acid, and sugar acids; monoacid oligomers such as blocked aliphatic dicarboxylic acids (such as the monomethyl ester of adipic or sebacic acid) or blocked Acid functional polyesters; or oligomeric polyesters such as poly(caprolactone) or poly(caprolactam), etc. In addition, a liquid monofunctional carboxylic acid can be used. The one acid species can also improve the optical properties of the resulting coating such as gloss, wrinkle and DOI, and can provide additional flexibility and/or impact resistance.

The powder coating composition may further comprise a carboxylic acid group-containing material selected from the group consisting of _C4-20 aliphatic polycarboxylic acids, polymeric polyanhydrides, low molecular weight polyesters having an average molecular weight of about 150-600, and mixtures thereof.

Usable aliphatic polycarboxylic acids include dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid and dodecanedioic acid. Preferably the dicarboxylic acid contains an even number of carbon atoms.

The coating composition may also contain certain other additives which are commonly incorporated into powder coating compositions, including pigments, flow control agents, anti-popping agents, powder flow additives and light stabilizers.

In order to provide a stable color to the powder coating composition, a pigment may be included in the coating composition, and the pigment usually contains about 1-50wt% based on the total weight of the powder coating composition. Pigments that can be used in powder coating compositions can be organic or inorganic and include lead silica chromate, titanium dioxide, ultramarine blue, phthalo green, carbon black, black iron oxide, chromium green oxide ), iron yellow and quinto red.

Suitable as flow control agents are acrylic polymers or copolymers such as polylauryl acrylate, polybutyl acrylate, poly(2-ethylhexyl) acrylate, poly(ethyl acrylate-co-2-ethyl acrylate hexyl ester), polylauryl methacrylate, polyisodecyl methacrylate, etc., also includes esters of fluorinated polymers such as polyethylene glycol or polypropylene glycol with fluorinated fatty acids, e.g. molecular weight greater than about 2500 Ester of Polyethylene Glycol and Perfluorooctanoic Acid. Polysiloxanes with a molecular weight greater than 1000 can also be used as flow control agents, such as polydimethylsiloxane or poly(methylphenyl)siloxane. Flow improvers are used to reduce surface tension when powders are heated and to eliminate arc craters. Typically, when a flow control agent is used, it is used in an amount of about 0.05-5% by weight (based on the total weight of the powder coating composition).

Anti-popping agents may be added to the composition to cause volatile components present to escape from the film during drying of the film. Benzoin is a particularly preferred degassing agent when used in an amount of about 0.5 to 3% by weight based on the total weight of the powder coating composition. The powder coating composition can also preferably contain a UV absorber such as TINUVIN ^(R) , which is a commercially available product and a registered trademark of Ciba-Geigy Corporation. When used, TINUVIN ^(R) generally contains about 0.5- 6wt% (based on the total weight of the powder coating composition).

In addition, the powder coating composition may contain fumed silica or the like as a powder flow additive in order to reduce powder clumping during storage. An example of fumed silica is the material sold by Cabot Corporation under the trademark CAB-O-SIL ^(R) . When powder flow additives are used, they are typically used in an amount of about 0.1 to 0.5 wt%, based on the total weight of the powder coating composition. Powder flow additives are typically added to particulate powder coating compositions after the particulate mixture has been prepared.

A thermosetting powder coating composition is prepared by melt blending the ingredients of the coating composition. Specifically, it can be accomplished by first blending in a high shear or high intensity dry blender such as a Henschell mixer. The mixture is then melt blended at about 80-130°C in an extruder such as a Werner-Pfleiderer ZK-30 twin-screw extruder. The extrudate is then cooled and pulverized into a powder. The powder coating composition can be applied directly to metal such as steel or aluminum, glass, plastic, or fiber reinforced plastic substrates.

Application of powders can be by electrostatic (corona discharge or triboelectric) spraying or by using a fluidized bed. Electrostatic spraying is preferred. The powder coating composition can be applied one or more times to achieve a cured film thickness of about 0.5-5 mils. Advantageously, in order to provide a high quality end product at a reasonable cost, the thickness of the powder coat is about 1.2-4 mils, preferably about 1.4-3 mils.

The substrate to be coated can be preheated prior to powder application if desired to promote more uniform powder deposition. After the powder has been applied, the powder-coated substrate can generally be baked at about 300-400°F (149-204°C) for 5-60 minutes, preferably about 20-40 minutes.

The following examples demonstrate the preparation of various hydroxyalkylamide curing agents, carboxylic acid functional polyester polymers, carboxylic acid functional acrylic polymers, which are treated with the monocarboxylic acids used in the preparation of the thermosetting powder coating compositions of the present invention .

These examples are intended to illustrate the invention, not to limit the scope or description of the invention, which is more clearly defined in the claims.

Example 1: Preparation of powder coating (colored white)

Pigmented powder coating compositions containing a β-hydroxyalkylamide crosslinker, a carboxylic acid-containing polyester and various levels of a monofunctional carboxylic acid were prepared. For comparison, a similar system was prepared without the monofunctional carboxylic acid, all values are percentages of the total formulation.

Note: 1. A polyester with an acid value of about 34, commercially available Grilesta V766-12, purchased from EMS-American Grilon Company. 2. Modaflow III is an acrylic acid copolymer on a silica support, available from Monsawto Corporation. The formulation ingredients were premixed for 1 minute at 180 rpm in a Henschel high intensity mixer and then extruded at 110°C in a Werner and Pfleiderer ZSK-30 extruder. The extrudate was then cooled, crushed, ground in a Micropul hammer mill, sieved through a 140 mesh screen, and electrostatically sprayed onto Bonderite 1000 substrate using a Volstatic gun. The powder coating was cured in a forced-air oven at 180°C for 20 minutes. The mechanical and optical properties of these coatings are listed in Table 1.

Example 2: Preparation of powder coating (colored white)

A pigmented powder coating composition has triglycidyl isocyanurate crosslinker, a carboxylic acid-containing polyester and various levels of a monofunctional carboxylic acid. For comparison, a similar system without the monofunctional carboxylic acid was prepared. All data are in percent of the total formulation.

Notes: ¹ A polyester having an acid value of about 34 is commercially available as Grilesta P7307.3, available from EMS-American Grilon.

² commercially available from Giba-Geigy under the name Araldite PT-810.

³ Modaflow III is an acrylic acid copolymer supported on a silica support, available from Monsanto.

The formulation ingredients were premixed for 1 min at 1800 rpm in a Henscher high-intensity mixer and subsequently extruded at 110°C in a Werner and Pfleiderer ZSK-30 extruder. The extrudate was then cooled, crushed, ground in a Micropul hammer mill, sieved through a 140 mesh screen, and electrostatically sprayed onto a Bonderite 1000 substrate using a Volstatic gun. The powder coating was cured in a blast oven at 180°C for 20 minutes. The mechanical and optical properties of these coatings are listed in Table 2.

Example 3: Preparation of powder coating (blue color)

A pigmented powder coating composition comprising a beta-hydroxyalkylamide crosslinker, a polyester containing carboxylic acid groups and a monofunctional carboxylic acid. For comparison, a similar system without the monofunctional carboxylic acid was prepared. All values are in percent of the total formulation.

Notes: ¹ A polyester having an acid value of about 34 is available from EMS-American Grilon under the designation Grilesta V76-2.

² Modaflow is an acrylic copolymer supported on a silica support, commercially available from Monsanto.

³ BT-417 is a phthalocyanine blue pigment previously obtained from Dupont.

The formulation ingredients were premixed for 1 minute at 1800 rpm in a Henschel high intensity mixer and subsequently extruded at 110°C in a Werner and Pfleiderer ZSK-30 extruder. The extrudate was then cooled to crush, ground in a Micropul hammer mill, sieved through a 140 mesh screen, and electrostatically sprayed onto a Bonderite 1000 substrate with a -Volstatic gun. The powder coating was cured in a blast oven at 180°C for 20 minutes. The mechanical and optical properties of these coatings are listed in Table 3.

Example 4: Preparation of powder coating (colored white)

A pigmented powder coating composition containing a beta-hydroxyalkylamide crosslinker, a carboxylic acid-containing polyester and various levels of benzoic acid as a monofunctional acid additive. For comparison, a similar system without the monofunctional carboxylic acid was prepared. All data values are percent values of the total formulation.

The formulation ingredients were premixed for 1 minute at 1800 rpm in a Henschel high intensity mixer and then extruded at 110°C in a Werner and Pfleiderer ZSK-30 extruder. The extrudate was then cooled, crushed, ground in a Micropul hammer mill, sieved through a 140 mesh screen, and electrostatically sprayed onto a Bonderite 1000 substrate with a -Volstatic gun. The powder coating was cured in a blast oven at 180°C for 20 minutes. The mechanical and optical properties of these coatings are listed in Table 4.

Embodiment 5: the preparation of acrylic powder coating

A pigmented powder coating composition containing a β-hydroxyalkylamide crosslinker, a carboxylic acid-containing acrylic polymer and 4% (based on acrylic resin) stearic acid as a monofunctional acid additive. For comparison, a similar system without the monofunctional carboxylic acid was prepared. All values are percentages of the total formulation.

Note:

1. An acrylic resin called SCX-815B, available from S.C. Johnson Company.

2. Modaflow is an acrylic acid copolymer on a silica support, available from Monsanto.

3. Resiflow P-67 is an acrylic flow aid available from Estron Chemical.

The formulation ingredients were premixed for 1 minute at 1800 rpm in a Henschel high intensity mixer and then extruded at 110°C in a Werner and Pfleiderer ZSK-30 extruder. The extrudate was then cooled, crushed, ground in a Micropul hammer mill, sieved through a 140 mesh screen, and electrostatically sprayed onto a Bonderite 1000 substrate with a -Volstatic gun. The powder coating was cured in a blast oven at 180°C for 20 minutes. The mechanical and optical properties of these coatings are listed in Table 5.

Embodiment 6: QUV-8 wind erosion resistance

Bonderite 1000 panels coated with the powder coating composition of Example 3 were placed in a QUV weatherometer equipped with a "B" ball (313 nm maximum diameter). The cycle of the weathering tester is light at 65°C for 8 hours, and condensation at 40°C for 4 hours. The 20 and 60°C gloss is read throughout the light cycle and gloss retention, characterized by time (hours) for a given gloss level, is calculated from the gloss measurements as a function of time. These data are listed in Table 6.

Experimental procedure

(1) The impact strength was measured using a Gardner impact tester.

Increasing amounts of impact were applied to the coated strips until the coating cracked. Impacts were made on the coated side of the plank, ie front impact, or on the coated side of the plank, ie reverse impact, and the results were reported in pounds per inch.

(2) The T-bend test consists of bending the coated strip (1 1/2″ x 12″) at 180°C, allowing the coated strip to overlap itself, and checking for cracking and delamination during bending.

(3) Attempt to scratch a mark on the coating, and the hardness of the first pencil that can scratch a mark on the coating is recorded as the pencil hardness of the film.

(4) Gloss at 20°C and 60°C was measured with a gloss meter manufactured by Gardner Instruments.

(5) Wrinkled skin is visually judged on the cured slats and divided according to the actual surface roughness.

(6) Determine the authenticity of the image by using a device that reflects a half-circle of the image or by varying the size of the image on the surface of the slat. The size at which the image is clearly visible on the plank determines the recorded DOI value.

Although the present invention has been described in detail with reference to the above specific embodiments, it is not meant to limit the scope of the present invention, but the following claims define the scope of the present invention.

Claims (13)

1, the powdered thermosetting compositions for coatings that has improved optical property, it comprises a kind of carboxylic acid group's of containing polyester, a kind of beta-hydroxy alkylamide solidifying agent, and a kind of its content is the monocarboxylic acid based material that contains of about 0.5-15wt% (based on polyester weight meter).

2, the composition of claim 1 further comprises a kind of monocarboxylic acid based material that contains, and this material is selected from stearic acid, tetradecanoic acid, palmitinic acid, phenoxy acetic acid, phenoxy propionic acid, Ba Dousuan, phenylformic acid and amygdalic acid; Aromatic acid comprises phenylformic acid, toluic acid (adjacent, and to), acetylsalicylic acid, Whitfield's ointment, methoxy benzoic acid (anisic acid), isopropyl acid and styracin; Ring grease acid comprises hexahydrobenzoic acid, Cyclopentane carboxylic acid, saccharic acid etc.

3, the composition of claim 2, wherein containing monocarboxylic acid based material is stearic acid.

4, the composition of claim 2, wherein containing monocarboxylic acid based material is phenylformic acid.

5, the composition of claim 2, wherein containing monocarboxylic acid based material is styracin.

6, the composition of claim 2, wherein containing monocarboxylic acid based material is saccharic acid.

7, the composition of claim 1, the polyester that wherein contains the carboxylic acid group are to be formed by many alcohol of aliphatic series or the many pure condensation reactions with aliphatic series or aromatic multi-carboxy acid and acid anhydrides of cyclic aliphatic, and the Tg of polyester is about 30-85 ℃, and its acid number is about 20-80.

8, the composition of claim 2, wherein, the polyester that contains the carboxylic acid group accounts for about 1-10wt% of vibrin weight.

9, the composition of claim 1, wherein, beta-hydroxy alkylamide has following structural formula

Wherein, R ₁Be H or C _1-5Alkyl; R ₂Be H, C _1-5Alkyl or

R wherein ₁Meaning the same, A is a chemical bond or monovalent or polyvalent organic group, this group self-saturating, undersaturated or fragrant hydrocarbon of deriving comprises the substituted hydrocarbon radical that contains 2-20 carbon atom, m equals 1-2, n equals 0-2, m+n is at least 2.

10, the composition of claim 9, wherein, the equivalence ratio of beta-hydroxy alkylamide and carboxylic acid is 0.6: 1-6: 1.

11, a kind of powdered thermosetting compositions for coatings with improved apparent character comprises a kind of carboxylic acid group's of containing vinylformic acid, a kind of beta-hydroxy alkylamide solidifying agent, and a kind of monocarboxylic acid based material that contains that accounts for the about 0.5-15wt% of acrylic resin weight.

12, the composition of claim 11, wherein, monocarboxylic acid accounts for about 1-10wt% of acrylic resin weight.

13, a kind of powdered thermosetting compositions for coatings with improved apparent character comprises a kind of carboxylic acid group's of containing polyester, a kind of epoxy functionalized crosslinking and curing agent, and a kind of monocarboxylic acid based material that contains that accounts for the about 1-10wt% of polyester weight.